EVOH and EVM in single- or multilayer products

ABSTRACT

The present invention relates to a single- or multilayer product containing α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the amount of vinyl acetate repeat units present in the α-olefin vinyl acetate copolymer is in the range from 35 to 99.99% by weight, and these repeat units have good flexibility which permits processing films or other thin-walled items which are transparent after stretching or thermoforming, and to a process for producing the same, and to their use as packaging films.

FIELD OF THE INVENTION

[0001] The present invention relates to a single- or multilayer productcontaining α-olefin-vinyl alcohol copolymers and at least oneα-olefin-vinyl acetate copolymer, wherein the amount of vinyl acetaterepeat units present in the α-olefin vinyl acetate copolymer is in therange from 35 to 99.99% by weight. These repeat units have goodflexibility which permits the processing of films or other thin-walleditems which are transparent after stretching or thermoforming, and to aprocess for producing the same, and to their use as packaging films.

BACKGROUND OF THE INVENTION

[0002] Shrink packaging, “skin-pack” system processes and stretchingprocesses are used in particular for packaging films. EVOH is a verybrittle material and the corresponding films have poor flexibility. Onthe other hand, EVOH films have excellent gas barrier properties, makingEVOH the preferred material for boundary layers in multilayer films.EVOH has also been proposed for fuel hoses.

[0003] WO-99/28124-A1 shows that stress-strain curves are highlydependent on the build of the film. High strain values may be achievedwith multilayer builds of up to 61 layers, and these are compared withthree layers. However, the technical requirements for producing a filmof this type are high, and therefore difficult to achieve withEVOH-containing films.

[0004] Examples of modifications to the EVOH resins using nylon-typepolymers are described in Ahn, Tae Oan; Kim, Chang Kee; Kim, Byung Kyu;Jeong, Han M O; Huh, Jung. Dep. Chem. Technol., Seoul National. Univ,Seoul, S. Korea. Polym. English. Sci. (1990), 30(6), 341-9. In Ahn,So-Bong; Jeong, Han M o, Department of Chemistry, University of Ulsan,Ulsan, S. Korea, Polymer (Korea) (1999), 23(6), 837-843 the miscibilityof PVPST (vinylpyridine-styrene copolymers) with EVOH is described.However, the effect on flexibility was not studied. MiscibleEVOH/polyvinylpyrrolidone mixtures are disclosed in Ahn, So-Bong, Jeong,Han MO. Department of Chemistry, University of Ulsan, Ulsan, S. Korea,Korea Polym. J. (1998), 6(5), 389-395.

[0005] EP-A1-0 309 095 describes blends of EVOH with certain amorphouspolyamides, but does not report any increase in the flexibility of theseblends compared with pure EVOH.

[0006] EP-A2-0 820 381 describes mixtures of EVOH with polar copolymers,such as ethylene-acrylate copolymer and ethylene copolymer, these havingbeen modified with maleic anhydride.

[0007] EP-A1-0 440 535 describes mixtures of EVOH with a PE of densityfrom 0.900 to 0.940 and with the reaction product of acarboxylic-acid-grafted polyolefin with an oligomeric polyamide.

[0008] EP-A1-1 022 309 describes mixtures of EVOH, ethylene-acrylatecopolymer and ethylene-acrylate-anhydride copolymer, which was reactedwith polyamides for the purpose of coinjection with PET to manufactureparisons for bioriented bottles.

[0009] WO-98/45367-A1 claims mixtures of EVOH with ethylene-vinylacetate copolymers for producing items with increased environmentalstress crack resistance, the ethylene-vinyl acetate copolymers usedhaving VA contents of up to about 30%. No particular requirements areplaced here on oxygen transmission or permeability.

[0010] U.S. Pat. No. 5,993,977 describes multilayer composites which,alongside a PE layer impermeable to water and a paper layer, also have alayer which is impermeable to gas and which is composed of a blend ofEVOH with a polar ethylene polymer. This polar ethylene polymer isregarded as a modified PE. However, the blend component claimed in thepresent invention is a vinyl acetate polymer, which has been modified ina nonpolar manner (with ethylene).

[0011] EP-A 0 333 443 discloses multilayer products whose layerstructure comprises three different ethylene-vinyl acetate copolymerlayers (EVM layers), a barrier layer, an adhesive layer and acopolyamide layer.

[0012] DE-A 26 44 209 discloses a composite film made from apolypropylene (PP) base film and from an intermediate layer of modifiedpolyethylene (PE) and finally from an outer layer of ethylene-vinylalcohol copolymer (EVOH). It circumvents the known difficulties withstretching of a EVOH layer by stretching the EVOH layer and theintermediate layer only in one direction, whereas the stretching of thePP film is biaxial. This requires the production of a cast PP film withsubsequent monoaxial stretching, its lamination to EVOH and anintermediate layer, and then the monoaxial stretching of this composite.A disadvantage of this process is that it is composed of more than onestep. This process cannot give biaxial stretching.

[0013] U.S. Pat. No. 4,400,428 discloses composite films, which comprisebiaxial polyamide films and also ethylene-vinyl alcohol copolymer layersand sealable layers.

[0014] EP-A 132 565 discloses oriented multilayer films which areproduced by coextruding polyamide films and ethylene-vinyl alcoholcopolymers and then are monoaxially stretched.

[0015] JP-A 2001 277 419 describes films which can be used for thepackaging industry and which comprise biaxially oriented nylon-6 filmsand a composition composed of polyurethanes, a two-layer polyurethanecomponent, and an LLDPE film. They have good resilience and lowpermeability.

[0016] JP-A 2001 277 417 discloses biaxially oriented nylon-6 filmsadhesive-bonded to unstretched polypropylene and having low oxygentransmission.

[0017] JP-A 2001 294 279 discloses other, very complicated systems wherea biaxially stretched nylon layer is provided with a polyurethane anchorlayer, with polyvinyl alcohol and with protective layers.

[0018] JP-A 09039172 teaches stretching EVOH biaxially and thensubjecting it to a corona surface treatment, laminating PE to both ofits sides, and providing it with a biaxially stretched polyamide layer.

[0019] JP-A 09 039 182 discloses the coextrusion of polyamide (PA) withPE for biaxially stretched films and lamination to EVOH, which alsocomprises some polyamide, no anchor layers are needed. However, thebarrier layer also has to be corona-treated.

[0020] WO 9 703 822 discloses films of high strength and low moisturetransmission, composed of a monoaxially stretched layer of polyamide andEVOH and of a biaxially oriented LLDPE layer. These two layers have tobe bonded by means of an intermediate polyurethane layer.

[0021] JP-A 08 207 927 discloses composite films with paper-likecharacter without aluminum foil, a thermoplastic layer being bonded to abiaxially oriented polyamide, or to PET, or to a polypropylene layer.Vapor deposition of SiO₂ then takes place. The remaining layer structurecomprises a EVOH or PVOH layer, which is finally bonded to two or morepaper layers.

[0022] JP-A 01 255 535 laminates a biaxially oriented polyamide film toa coextruded film made from ethylene-vinyl alcohol copolymer and anionomer (adhesive layer), to obtain a shrink film.

[0023] JP-A 06255054 discloses 3-layer films whose first layer comprisesnylon-6, while the second comprises a blend of semiaromatic polyamide ofMXD nylon 6007 type with ethylene-vinyl acetate copolymer and the thirdcomprises a mixture of the materials of the first two layers. A smallamount of maleic-anhydride-grafted ethylene-propylene copolymer is alsoadded to the polyamide layers here in order to improve resistance tofracture on creasing.

[0024] Biaxially oriented polyamide blends (nylon-6,6 and MXD,6) arealso disclosed in EP-A 0 540 293 as having better splittability.

[0025] JP-A 04 169 231 discloses a 3-layer film structure with acopolyamide layer, with an ethylene-vinyl alcohol copolymer layer andwith another copolyamide layer. This film can be stretched biaxially,but only in a ratio of 3:1. When a polyamide of nylon-6 type is used thefilm becomes wrinkled after stretching. The implication is thatcombinations of high-melting polyamide and EVOH cannot be stretchedbiaxially without phase separation.

[0026] JP-A 04 131 237 discloses films made from ethylene-vinyl alcoholcopolymer and nylon-6/12 blends including LiCl, these being laminated tobiaxially oriented nylon-6 and to unstretched polypropylene in order toobtain films impermeable to water vapor.

[0027] JP-A 01 221 241 teaches stretching a PET film biaxially and thenlaminates it to a composite film made from EVA/EVOH/nylon/EVA, thecomposite films then being subjected to corona treatment. According toJP-A 01 221 241, EVA means an ethylene-vinyl acetate copolymer whosevinyl acetate content is not more than 35% by weight.

[0028] JP-A 62 083 144 discloses a packaging film made from a biaxiallystretched ethylene-vinyl alcohol copolymer film which, after thermaltreatment, is laminated to a biaxially stretched polypropylene film. Apolyurethane layer is also required here as adhesive layer.

[0029] JP-A 09 220 761 discloses stretched PA/EVOH/PA films. A specificheat-conditioning program has to be complied with here prior to thestretching step.

[0030] JP-A 1998 003 5669 discloses PA and EVOH as starting materialsfor film extrusion processes. However, the product is merely doublelayers, which then can be stretched only after treatment in water.

[0031] In Polym. Networks Blends, 7 (4), 139-46 (1997), Nir et al.describe blends of ethylene-vinyl alcohol copolymer with anethylene-vinyl acetate copolymer whose vinyl acetate content is 9% byweight.

[0032] The prior art discussed shows that a particular pretreatment isessential to permit stretching or thermoforming of a multilayer product,which contains a thermoplastic elastomer, such as polyamide orpolypropylene, and ethylene-vinyl alcohol copolymer (EVOH). Although thebiaxial stretching of films which comprise only polyamide is a wellknown process, the stretching of EVOH is, on the other hand, difficult,since it is very brittle and, due to its rapid crystallization, has onlyvery restricted processing latitude. Therefore there is insufficientprovision for the manufacture of thin, stretched film structures, unlessthey are manufactured by a multistage process composed of many steps.The many steps lead to disadvantages in cost-effectiveness.

SUMMARY OF THE INVENTION

[0033] An object of the present invention was to find blend componentsfor EVOH, permitting stretching of the mixture which contain a blendcomponent and EVOH. Another object of the present invention was toretain the underlying mechanical properties of the EVOH and its goodbarrier property.

[0034] A good barrier property primarily means that the product does notexhibit good oxygen transmission. However, a good barrier property alsomeans the ability to maximize the prevention of access of othermolecules, such as odorous constituents and chemicals, from the wares tobe protected.

[0035] At the same time, the adhesion properties of the EVOH filmsshould generally be improved in order to gain options for themanufacture of relatively simple multilayer films. Another object of thepresent invention is therefore to provide a multilayer product which,without further pretreatment, is transparent after the stretchingprocess and also has low oxygen transmission.

[0036] Accordingly, the present invention is directed to a single- ormultilayer product containing one or more α-olefin-vinyl alcoholcopolymers and at least one α-olefin-vinyl acetate copolymer, whereinthe amount of vinyl acetate repeat units present in the α-olefin vinylacetate copolymer is in the range from 35 to 99.99% by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 illustrates the mechanical values from the extruded filmsof 20 μm thickness from Examples 14-18.

[0038]FIG. 2 illustrates the VA content in ethylene-vinyl acetate vs.the oxygen transmission standardized to 100 μm at 0% relative humidity,as reported in Table 2.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The single-layer product of the present invention preferably usesfilms containing α-olefin-vinyl alcohol copolymers and at least oneα-olefin-vinyl acetate copolymer, whose content of vinyl acetate repeatunits is in the range from 35 to 99.99% by weight.

[0040] The α-olefin included in the films of the single-layer product ofthe present invention preferably contain ethylene, propene, n-butene,isobutene, pentene, hexene, 1-hexene, heptene, octene, 1-octene, or amixture of these.

[0041] The films of the single-layer product of the present inventionpreferably contain α-olefin-vinyl acetate copolymer having at least 45%by weight of vinyl acetate repeat units.

[0042] The films of the single-layer product of the present inventionmore preferably contain α-olefin-vinyl acetate copolymer having at least65% by weight of vinyl acetate repeat units.

[0043] The process for producing the single-layer product of the presentinvention includes mixing the copolymer in a mixer with the otherconstituents.

[0044] The multilayer product of the present invention preferablycontains at least one layer A and at least one layer B, where A containsa thermoplastic polymer and B contains an α-olefin-vinyl alcoholcopolymer and an α-olefin-vinyl acetate copolymer whose vinyl acetatecontent is in the range from 35 to 95% by weight.

[0045] The thermoplastic polymer in the multilayer product of thepresent invention is preferably polyamide or polypropylene.

[0046] The α-olefin-vinyl alcohol copolymer used in the multilayerproduct is preferably ethylene-vinyl alcohol copolymer whose ethylenecontent is in the range from 20 to 75 mol %.

[0047] The α-olefin-vinyl acetate copolymer used in the multilayerproduct of the present invention is preferably ethylene-vinyl acetatecopolymer.

[0048] The preferred layer sequence in the multilayer product of theinvention is A,B,A.

[0049] The layer sequence of the multilayer product of the invention ispreferably polyamide, layer B, polyamide.

[0050] The layer sequence of the multilayer product of the invention ispreferably polypropylene, layer B, polypropylene.

[0051] The multilayer product of the present invention preferably hasthe layer sequence polypropylene, layer B, polypropylene, and betweeneach pair of layers another layer of a polymer has been introduced andserves to improve the cohesion of the composite.

[0052] The multilayer product of the present invention is advantageouslyproduced by coextrusion or by lamination.

[0053] The single- or multilayer product of the present invention isuseful as a packaging material.

[0054] The multilayer product can readily be stretched to give thinfilms and once stretched has a high oxygen barrier, and tear resistance,penetration resistance and chemical resistance. This chemical resistanceshown by the multilayer product applies with respect to animal andvegetable fats and oils and also to fuels and lubricants. Goodmechanical properties are also found, such as high tensile strengths,elongations, module of elasticity and flexural strengths.

[0055] Another advantage of the multilayer product is that it opens upother processing opportunities, such as vacuum forming, blown-filmprocesses, and thermoforming, and it is therefore also possible to moldthree-dimensional moldings from the product of the invention. Thebarrier layer of the invention may be extruded relatively simplytogether with other layers, since flat-film dies achieve more uniformdistribution. Brittleness of the barrier layer is lower in the productof the invention, achieving better resistance to fracture on creasing.

[0056] The α-olefin-vinyl alcohol copolymers of the single- ormultilayer product of the present invention are copolymers of α-olefinswith vinyl alcohol. These are preferably prepared by hydrolyzingα-olefin-vinyl acetate copolymers. The α-olefin-vinyl alcohol copolymersare preferably selected in accordance with the requirements placed uponthe barrier property of the item to be produced. The α-olefin contentsof the α-olefin-vinyl alcohol copolymers are preferably from 20 to 75mol %, more preferably from 25 to 60 mol % and most preferably from 25to 50 mol %.

[0057] A high degree of hydrolysis is desirable, preferably from 90 to99.9%.

[0058] Suitable α-olefins include any of the α-olefins known to theperson skilled in the art, for example ethene, propene, n-butene,isobutene, pentene, hexene, 1-hexene, heptene, octene, 1-octene andhigher homologues of these. These may also bear substituents, inparticular C₁-C₅-hydrocarbon radicals. Ethene and propene are preferredα-olefins.

[0059] In the case of ethylene-vinyl alcohol copolymers, there may alsobe other α-olefins or derived monomers present, albeit in amounts ofless than 10 mol %, alongside ethylene units and vinyl alcohol units.

[0060] The molecular weight of the α-olefin-vinyl alcohol copolymer ispreferably determined indirectly via MFI measurements and is importantfor processing performance. The flowability of the products, expressedin terms of MFI (ASTM D1238, 190° C., 2.16 kg load), is preferably from0.5 to 100 g/10 min, more preferably from 1 to 50 g/10 min.

[0061] The selection of the α-olefin-vinyl acetate copolymer of thepresent invention depends on the requirements placed on oxygentransmission. This becomes smaller as the VA content of theethylene-vinyl acetate copolymer used becomes higher. Particularly highflexibility, and therefore stretchability or thermoformability, isachieved if the VA content is not excessively high. For example, purevinyl acetate homopolymer proves to be too brittle for someapplications.

[0062] Particularly high impermeability to odor can be achieved withethylene-vinyl acetate copolymers of the invention as a blend componentif use is made of grades which preferably have high VA content. Thesehave low swellability and, with this, low permeability to nonpolar orlow-polarity compounds.

[0063] It is advantageous to use α-olefin-vinyl acetate copolymers whichhave only low, or no, residual crystallinity of poly-α-olefin sequences.

[0064] The α-olefin-vinyl acetate copolymers of the single- ormultilayer product of the present invention preferably contain from 35to 98% of vinyl acetate repeat units.

[0065] Suitable α-olefins include any of the α-olefins known to theperson skilled in the art, for example ethylene, propene, n-butene,isobutene, pentene, hexene, 1-hexene, heptene, octene, 1-octene andhigher homologues of these. Of course, these may also bear substituents,such as C₁-C₅-hydrocarbon radicals. Ethylene and propene are preferred.

[0066] Examples of preferred ethylene-vinyl acetate copolymers areavailable commercially from Bayer AG with the trade name LEVAPREN® orLEVAMELT®.

[0067] Preferred α-olefin-vinyl acetate copolymers are Levapren® 500 HV,Levapren® 600 HV, Levapren® 700 HV and Levapren® 800 HV. These polymerscontain, respectively, 50±1.5% by weight of vinyl acetate, 60±1.5% byweight of vinyl acetate, 70±1.5% by weight of vinyl acetate, 80±2.0% byweight of vinyl acetate.

[0068] The ethylene-vinyl acetate copolymers which may be used accordingto the present invention have MFI values of from 0.5 to 150, preferablyfrom 1 to 100, more preferably from 1 to 50, measured to DIN 53 735 at130° C. with a load of 2.16 kg. The selection of the MFI value dependson the processing requirements.

[0069] Preferred α-olefin-vinyl acetate copolymers have an average(number-average) molar mass (determined by GPC) in the range from 50kg/mol to 500 kg/mol, and Mooney viscosities to DIN 53 523 ML 1+4 at100° C. in the range from 3 to 50, preferably from 4 to 35 Mooney units.

[0070] The α-olefin-vinyl acetate copolymers may also be used in theform of a mixture of two or more different α-olefin-vinyl acetatecopolymers selected from those mentioned.

[0071] The α-olefin-vinyl acetate copolymers to be used for the-α-olefin-vinyl alcohol copolymer/α-olefin-vinyl acetate copolymerblends of the present invention are preferably prepared by the solutionprocess described in EP 341 499, EP 510 478 and DE 3 825 450. Thesolution processes at pressures of from 100 to 700 bar and attemperatures of from 50 to 150° C., using free-radical initiators. Anadvantage of this process is that it produces gel-free products inwhich, no other auxiliaries, such as emulsifiers are present.

[0072] The α-olefin-vinyl alcohol copolymer/α-olefin-vinyl acetatecopolymer blends of the single- or multilayer product of the presentinvention preferably contain from 50 to 95% by weight of α-olefin-vinylalcohol copolymers and from 5 to 50% by weight of α-olefin-vinyl acetatecopolymers.

[0073] The α-olefin-vinyl acetate copolymers in layer B of the productof the present invention preferably contain from 35 to 98% of vinylacetate repeat units.

[0074] The α-olefin-vinyl acetate copolymers can be prepared using thecopolymerization processes known in the industry, for example byhigh-pressure copolymerization with the aid of initiators whichdecompose to give free radicals, by copolymerization using Ziegler, orZiegler-Natta catalysts, or using Phillips catalysts, or else bycopolymerization using metallocene-containing catalysts. Thiscopolymerization may take place in the gas phase, in solution or in asuspension, either continuously or else batchwise.

[0075] Preparation processes of this type are known to the personskilled in the art and working in the field of rubber technology, andare described by way of example in V. E. Rohde, 141. Meeting at the ACS,Louisville 1992, and also in EP-A-0 341 499, DE-A-3 825 450 and EP-A-0510 478. The solution polymerization without addition of otherauxiliaries is the preferred process for the ethylene-vinyl acetatecopolymers to be used according to the present invention.

[0076] The α-olefin-vinyl acetate copolymers/α-olefin-vinyl alcoholcopolymers are preferably used in pure form. However, it is alsopossible to use blends with other polymers, such as polyamides. Mentionmay be made of polyamide resins of the nylon-6, nylon-6,6, nylon-4,6,nylon-11, nylon-12, nylon-6,10, nylon-6,12, nylon-6/6,6 copolymer,nylon-6/6,6/6, 10 copolymer, nylon-MXD,6, nylon-6,T, nylon-6/6,Tcopolymer, nylon-6,6/PP copolymer, and nylon-6,6/PPS type. Additions ofsuitable polyesters, e.g. of phthalate type, are also conceivable.

[0077] These additions may make up as much as 30% of the blend of thepresent invention.

[0078] Elastomers may also be added to the α-olefin-vinyl acetatecopolymers/α-olefin-vinyl alcohol copolymers, and should have minimumgas transmission. Examples of these include butyl rubber, butyl rubberwith p-alkylstyrene, and halogenated derivatives of these. The contentshould not exceed 30% within the mixture. It may then be necessary touse other compatiblizers, e.g. as described in EP-A1-0 722 850.

[0079] Additives may likewise be used in order to provide single- ormultilayer products for specific final applications. These additives maybe pigments, dyes, plasticizers, fillers, stabilizers, agents to absorbUV radiation, antioxidants, processing oils, or the like. The amount ofadditive used may vary in the range from 0.1 to 50% by weight, dependingon the intended final application. It is preferable that none of theadditives used absorb a significant amount of radiation close to thewavelength of the maximum absorption of any photocrosslinking agent,which may also be present in the film.

[0080] The single- or multilayer product of the invention may moreoveralso contain conventional fillers, such as talc, barite or kaolin orcarbon black.

[0081] It is, of course, possible to modify the properties of thesingle- or multilayer product of the present invention by addinglamellar particles, such as muskovites or hydrotalcite, as mentioned inEP-A1-0 309 095. These lamellar fillers reduce oxygen transmission. Theα-olefin-vinyl acetate copolymers used increase the ease ofincorporation of mineral pigments of this type. An upstream mixing stepmay also be used to add these to the α-olefin-vinyl acetatecopolymers/α-olefin-vinyl alcohol copolymers, and the amounts may berelatively large.

[0082] If EVOH-based barrier layers are used in shrink films,irradiation is frequently carried out prior to shrinking. This type ofradiation crosslinking, as described in DE-A1-198 34 580, can be carriedout using the blends of the present invention.

[0083] The barrier properties of the films of the present invention maybe further improved by applying a siloxane-based coating, as describedin EP-A1-0 476 202.

[0084] It is often advantageous for the film also to contain aphotocrosslinking agent, which is activated by actinic radiation,typically after the coating of the polymer. Suitable photocrosslinkingagents include, but are not restricted to, (a) aldehydes, such asbenzaldehyde, chromophor-substituted acetaldehyde and substitutedderivatives of these, (b) ketones, such as acetophenone, benzophenoneand substituted derivatives of these, e.g. Sandoray™ 1000 (SandozChemicals, Inc., Charlotte, N.C.), (c) quinones, such as benzoquinone,anthraquinone and substituted derivatives of these, (d) thioxanthones,such as 2-isopropylthioxanthone and 2-dodecylthioxanthone and (e)certain chromophor-substituted halomethyl-sym-triazines, such as2,4-bis(trichloromethyl)-6-4′-methoxyphenyl-s-triazine and2,4-bis(trichloromethyl)-6-3′,4′-dimethoxyphenyl-s-triazine. Since manytriazines of this type produce HCl during activation, it can also beuseful to add a basic compound to the polymeric composition. The amountpresent of the photoactive crosslinking agent is generally in the rangefrom 0.005 to 2% by weight, preferably from 0.01 to 0.5% by weight, andmore preferably from 0.05 to 0.15% by weight of the copolymer.

[0085] However, any crosslinking required may also take place by meansof high-energy radiation, such as α-, β- or γ-radiation, in the absenceof crosslinker.

[0086] The present invention also provides a process for producing thesingle- or multilayer product of the present invention, wherein theα-olefin-vinyl acetate copolymer with the α-olefin-vinyl alcoholcopolymer is mixed in a mixer with the other constituents.

[0087] Suitable mixtures of the α-olefin-vinyl acetate copolymers andα-olefin-vinyl alcohol copolymers may be prepared using any suitablemixing method, as long as the mixtures obtained are macroscopicallyhomogeneous. Examples of suitable mixing apparatus are Banbury mixers,rolls and preferably extruders. On-line mixing operations areparticularly advantageous here, e.g. those in the mixing zone of a filmextruder without any other specific precautions. Where appropriate, thesuitability of the planned mixing step needs to be checked byappropriate preliminary experiments. Dry blending of the materials inpellet form is advantageous for ensuring a constant mixing ratio.

[0088] The single- or multilayer product of the present invention issuitable for application to a suitable substrate to produce packagingfilms, such as barrier films. For example, as described in EP-A1-0 545312, it is possible to extrude a 5-layer film whose innermost layer iscomposed of the single-layer product of the present invention, each ofthe two sides of which have been surrounded by another intermediatelayer and by an outer layer.

[0089] Examples of materials of which these layers may be composed arenon-inventive ethylene-vinyl acetate copolymers having VA contents offrom 5 to 30%.

[0090] Suitable substrates include polyolefin films (e.g. polyethylenefilms and propylene films), preferably corona-treated polyolefin filmsand α-olefin-vinyl alcohol films, more preferably ethylene-vinyl alcoholfilms (EVOH).

[0091] As barrier layer, the copolymer mixture of the present inventionhas higher adhesion to intermediate or outer layers of this type,permitting the structure of the film to be simplified by omitting alayer.

[0092] The single-layer product of the present invention opens up thepossibility of using markedly fewer layers to achieve adequate adhesionto backing films, and other processing functionalities, such assealability.

[0093] In multilayer films, the products of the present invention mayalso be used as other layers beside the barrier layer. High tack canproduce particularly good bonds to non-polar backing films, such as PPor polyolefins in general.

[0094] It is also possible to use the single-layer products of thepresent invention as an adhesive layer. This can be used as anintermediate layer between EVOH and, for example, a polyolefin backinglayer. The high tack of the film of the present invention is utilizedhere. For this type of application, the mixing ratio may be changed inthe direction of ethylene-vinyl acetate copolymers (EVM), examples beingfrom 20/80 to 80/20 EVM/EVOH. This adhesive layer then likewise makes amuch greater contribution to barrier action than typical EVA adhesivelayers having VA contents of up to 30%.

[0095] The field of application of the single- or multilayer products ofthe present invention also extends generally to layers with barrieraction.

[0096] These also include hoses, or lines for organic solvents, such asfuels. For example, as mentioned in EP-A1-0 878 509, fuel pipes can bemanufactured using a layer of the single- or multilayer product.Radiation-crosslinking may then follow in order to achieve higherresilience and extensibility.

[0097] The single- or multilayer product of the present invention mayalso be used to produce tank liners. For this, the preferablysingle-layer product is applied before any crosslinker which may be usedto the, preferably primed, surface of a suitable underlayer (i.e. of asubstrate).

[0098] Many different processes may be used to apply the preferablysingle-layer product to a substrate (e.g. a belt underlayer), and theseinclude solution coating, solution spraying, emulsion coating, gravuracoating, and other processes known to persons skilled in the art.

[0099] Another preferred method of producing the single- or multilayerproduct is coextrusion coating, usually on a coating plant using amolten film of the α-olefin-vinyl acetate copolymer/α-olefin-vinylalcohol copolymer, the film being melted in an extruder and applied viaa slot die to a substrate which may be composed of one or more polymerlayers. The resultant composite is then cooled and smoothed in a coolingand pressure-roll unit. The composite web is then wound up at anappropriate winding unit.

[0100] The operations carried out in the laminating process, which isalso preferred and is similar to the coating process, are againapplication of the coating composition to the backing web, smoothing andcooling, draw-off and wind-up. In the actual extrusion-laminationprocess, a prefabricated backing web is made to run into asmoothing-roll stand which has 4 rolls. During this process, the backingweb is coated, prior to the first nip, with a melt film, which is meltedin an extruder and discharged via a slot die. A second prefabricated webis made to run in prior to the second nip. During passage through thesecond nip, the entirety of the resultant composite is smoothed and thencooled, drawn off, and wound up at a winding unit.

[0101] In the blowing/slot die extrusion process, also preferred, theα-olefin-vinyl acetate copolymer/α-olefin-vinyl alcohol copolymer andvarious polymers are generally first melted in various extruders undersuitable conditions, and then combined in the form of the melt streams,a multilayer melt stream being shaped in the extrusion die. This isfollowed by the discharge, draw-off and cooling of the multilayer meltweb comprising the film, and the wind-up of the composite. A compositefilm is thus obtained. It is preferable here to use the slot dieextrusion process.

[0102] Suitable polymers for these processes include α-olefin-vinylalcohol copolymer/α-olefin-vinyl acetate copolymer blends withthermoplastic polymers. The multilayer product of the present inventioncontain at least one layer A and one layer B, wherein A contains athermoplastic polymer. Thermoplastic polymers include any desiredpolymers, preferably those, which can be stretched biaxially.

[0103] Preferred thermoplastic polymers are polyamides, polypropylene,polystyrene, polycarbonates, polyesters, polyethylene terephthalate, andpolybutylene terephthalate.

[0104] More preference is given to the use of polyamides orpolypropylene. Preferably, layer A has more than 50% by weight ofpolyamide or more than 50% by weight of polypropylene. More preferably,layer A has from 60 to 100% by weight of polyamide or from 60 to 100% byweight of polypropylene. The layer A preferably contains polypropylenewhose melting point is in the range from 130° C. to 165° C. Morepreference is given to isotactic polypropylene with a crystallinefraction of more than 50%.

[0105] The layer A preferably contains polyamides with a melting pointin the range from 170 to 230° C.

[0106] Polyamides mean polymers whose internal linking is via the amidegroup —NH CO— (see also Kunststoff-Handbuch [Plastics handbook] VolumeVI, Polyamide [Polyamides], Carl Hanser Verlag, Munich, 1966). Adistinction is made between two groups of polyamides:

[0107] 1) built up from a monomer via polycondensation ofα-aminocarboxylic acids or polymerization of their lactams to givenylon-6 type

[0108] 2) built up from two monomers (diamines and dicarboxylic acids)by polycondensation to give the nylon-6,6 type (Gnauck, Fründt: Einstiegin die Kunststoffchemie [Introduction to plastics]. Carl Hanser Verlag,Munich, 1991).

[0109] Preferred polyamides are conventional polyamides, in particularnylon-6, but also copolyamides, nylon-6 with copolyamides, which can beprepared by polycondensing or, respectively, polymerizingpolyamide-forming starting materials.

[0110] Preferred polyamide-forming starting materials, besidescaprolactam, include other lactams, such as laurolactam,ω-aminocarboxylic acids, 11-aminoundecanoic acid, and also mixtures ofequivalent amounts of one or more dicarboxylic acids, preferably adipicacid, sebacic acid, azeleic acid, dodecanedioic acid, isophthalic acidor terephthalic acid, with one or more diamines, such ashexamethylenediamine, 1,4-diaminobutane,3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine),4,4′-diaminodicyclohexylmethane, 4,4′-diamino-2,2-dicyclohexylpropane,m-xylylenediamine, 1,6-diamino-2,2,4-trimethylhexane,2,2,4-trimethylhexamethylenediamine, or2,4,4-trimethylhexamethylenediamine.

[0111] Polyolefins of this type may be prepared by polymerizationmethods known to the person skilled in the art, for example byZiegler-Natta polymerization, by polymerization with the aid of Phillipscatalysts, by high-pressure polymerization or by polymerization with theaid of metallocene-containing catalysts.

[0112] The coating/extrusion processes are generally carried out attemperatures in the range from 170 to 300° C., at pressures of from 250to 400 bar and with average retention times of from 5 to 20 min. Sincethe α-olefin-vinyl acetate copolymers/α-olefin-vinyl alcohol copolymershave high tendency to adhere to any contact surfaces, it can beadvantageous to coat the rolls used for producing the composites, andalso the draw-off rolls, with a material which is antiadhesive withrespect to the copolymers, both in the melt and in the single- ormultilayer product of the invention, e.g. with polytetrafluoroethylene.This permits web tensions to be maintained which are appropriate, interalia, for satisfactory winding of the composites.

[0113] The films thus obtained may advantageously be used as packagingfilms with barrier properties with respect to air, oxygen, odors, etc.

[0114] To produce the transparent films, the films are stretched.Besides the preferred simultaneous biaxial stretching process,sequential stretching is also possible.

[0115] For the stretching process, preferably the biaxial stretching ofthe product of the present invention, the procedure may be as in thepatent specifications DE 3 529 586, DE 3 042 884 and DE 2 845 793.

[0116] Stretched products of the present invention may also be subjectedto a downstream heat-treatment step in order to minimize shrinkage(particularly hot-water shrinkage). This step may also be carried out inan inert gas atmosphere, as described in DE-A 3 042 884, in order toavoid yellowing.

[0117] In the case of a biaxially stretched product, shrinkage may becontrolled by means of a specific cooling program, as described in DE-A2 845 793.

[0118] The stretching for the packaging material made from the productof the invention may also take place starting with the bubble(“double-bubble”).

[0119] It is advantageous for another layer C to be applied to themultilayer product of the present invention and permit sealability. Thislayer C preferably contains a copolymer of ethylene with another monomerselected from the group consisting of α-olefins, vinyl acetate andacrylic acid. Preference is given to ethylene-α-olefin copolymers whosedensity is below 0.92 g/cm³. Preferred ethylene-vinyl acetate copolymersare those whose vinyl acetate content is not more than 20% by weight.Preferred ethylene-acrylic acid copolymers have acrylic acid content ofnot more than 10% by weight. The sealable layers may be appliedsubsequently, preferably by lamination, but may also be introduced atthe outset by coextrusion, and then passed through the stretchingprocess.

EXAMPLES

[0120] 1. Materials:

[0121] EVOH ethylene-vinyl alcohol copolymer having 44 mol % of ethyleneavailable from Kuraray.

[0122] Levapren® 400, ethylene-vinyl acetate copolymer having 40% byweight of vinyl acetate, Mooney value ML 1+4,100° C. of about 23, MFI of1.5, available from Bayer AG.

[0123] Levapren® 600 HV, ethylene-vinyl acetate copolymer having 60% byweight of vinyl acetate, Mooney value ML 1+4, 100° C. of about 27, MFIof 3, available from Bayer AG.

[0124] Levapren® 800 HV, ethylene-vinyl acetate copolymer having 80% byweight of vinyl acetate, Mooney value ML 1+4,100° C. of about 25, MFI of4, available from Bayer AG.

[0125] Levapren® 700 HV, KA 8865 grade, ethylene-vinyl acetate copolymerhaving 70% by weight of vinyl acetate, MFI of 3.5, available from BayerAG.

[0126] EVM 95, ethylene-vinyl acetate copolymer having 95% by weight ofvinyl acetate, MFI of about 8, prepared as in Example 1.

[0127] AZDN V64 azoinitiator, 2,2-azobisisobutyronitrile, available fromElf Atochem.

[0128] The MFI was measured to DIN 53735, the conditions being 190° C.and 2.16 kp.

[0129] Preparation of EVM 95:

[0130] Ethylene and vinyl acetate is polymerized in a batch reactor insolution with free-radical initiation.

[0131] A 5 l reactor was charged with a solution of 1,114 g of vinylacetate (VA) in 890 g of tert-butanol, and with a solution of 1 g ofADZN V64 azoinitiator in 50 ml of tert-butanol, and inertized byrepeated introduction of nitrogen under pressure followed bydepressurization. Ethylene was then introduced under pressure until thepressure was 6 bar. The mixture was then brought to a reactiontemperature of 58° C. and the pressure was increased to, and held at, 8bar, ethylene being supplemented as required by consumption.

[0132] Five hours after the start of the polymerization, 24.6% solidswas determined by taking a specimen, the reactor was brought to roomtemperature, excess ethylene was removed by depressurization, and themixture was discharged. The polymer was obtained by drying in a vacuumdrying cabinet to constant of weight. The glass transition temperatureof the product, determined by DSC, was 34.3° C. The VA content was 95%(determined by ¹H NMR).

Examples 1 to 13 (Extrusion Examples)

[0133] Extruder (Brabender Plasti-Corder and laboratory extruder) withL/D ratio of 30/25 D with slot die. The materials used were fed inpellet form and the temperature profile set was 165° C., 170° C., 175°C. and 180° C., and the pressures set were from 45 to 60 bar. Thethickness of the films was set via the throughput and via the draw-offrate. The film was cooled on a chill roll (water cooling) and wound upvia two or more deflector rolls or taken off in the form of individualstrips.

[0134] Polymer blends were prepared in the form of mixtures of pellets,and introduced directly to the extruder. The mixing action in theconveying extruder was itself sufficient to achieve homogeneous blends.

[0135] The resultant films were tested mechanically and for oxygentransmission. TABLE 1 Mechanical values for films Max F min F maxExample Material Thickness Tension D D 1 EVOH 31 μm  35-50     37 Mpa 46MPa comparison MPa 85% 190% 2 EVOH 205 μm   45-50     49 Mpa 62 MPacomparison MPa 300% 330% 3 Blend 55 μm 23 MPa    17 Mpas  26 MPa 85%EVOH 170% 220% 15% Levapren ® 800 HV 4 Blend 80 μm 25 MPa     29 Mpa 34MPa 70% EVOH 280% 290% 30% Levapren ® 800 HV 5 Blend 130 μm  33 MPa    40 Mpa 47 MPa 70% EVOH 325% 360% 30% Levapren ® 400 6 Blend 122 μm 34 MPa     40 Mpa 46 MPa 85% EVOH 320% 360% 15% Levapren ® 400 7 Blendof 70%  5 μm 20 MPa     20 Mpa 20 MPa EVOH 26% 37% with 30% EVM 95 8EVOH 70% 65 μm 34 MPa     35 Mpa 42 MPa 30% EVM 95 240% 280%

[0136] The tensile tests show that it is difficult to obtainreproducible strengths or elongations when tension is applied to pureEVOH films. For example, the breaking strengths of specimens of the samefilm can vary very markedly, and the same applies to the elongations.This makes it very difficult to produce monoaxially stretched orbiaxially stretched films.

[0137] In contrast, the blends with ethylene-vinyl acetate copolymerprepared in the examples gave films with greater reproducibility intensile strain values.

[0138] The film of Example 4 (blend of 70% EVOH and 30% of Levapren®400)had a distinctly tacky feel. The surface of the film was studied by IR,and comparison with the individual components revealed that the materialpresent at the surface was almost exclusively Levapren®400. From this itcan be concluded that, at least for EVA with 40% of VA as blendcomponent in EVOH, partial incompatibility is present at least underextrusion conditions, and this mixture is therefore not preferable.

[0139] Determination of Oxygen Transmission:

[0140] The measurements were made using an OX-TRAN test device from thecompany Mocon, to DIN 53380 Part III.

[0141] Table 2 shows the oxygen transmissions of various ethylene-vinylacetate copolymers at various relative humidities, the vinyl acetatecontents being varied. The oxygen transmissions fall with rising vinylacetate content, but the level of values for EVOH is not achieved. TABLE2 Determination of oxygen transmission for ethylene-vinyl acetate films,all at 23° C. Oxygen Stan- trans- dardized missions to 100 μ Relativecm³/(m²d Cm³ 100 μ/ Exp. Type Thickness humidity bar) (m² d bar) 9EVM-95  272 μm 0 104 282 50 159 432 100 298 810 10 Levapren ® 64.6 μm 01200 775 800 HV 50 1390 897 100 1880 1210 11 Levapren ® 42.5 μm 0 52202220 50 5790 2460 100 7690* 3270 700 HV 54.1 μm 0 4080 2210 50 4300 2330100 5710* 3090 12 Levapren ® 74.0 μm 0 33600 24860 50 29800 22050 10019500 14430 400 70.7 μm 0 12400 8770 50 11900 8410 100 10300 7280

[0142] The values standardized to 100 μm are plotted graphically in FIG.2. TABLE 3 Determination of oxygen transmission of EVOH films, all at23° C. Oxygen trans- Standardized missions to 100μ Relative cm³/(m² dcm³ 100μ/ Exp. Type Thickness humidity bar) (m² d bar) 3 Blend 59.4 μm 01.94 1.15 85% EVOH 56.1 μm 0 1.76 0.99 15% 59.4 μm 50 1.38 0.82Levapren ® 56.1 μm 50 1.40 0.79 800 HV 59.4 μm 100 43.9 26.1 56.1 μm 10042.8 24.0 13 Blend 41.4 μm 0 0.41 0.17 85% EVOH 34.7 μm 0 0.53 0.18 15%EVM 41.4 μm 50 0.29 0.12 95 34.7 μm 50 0.39 0.14 41.4 μm 100 8.48 3.5134.7 μm 100 9.75 3.38 From Comparison   25 μm 0 0.72 0.18 EP- EVOH E 753.29 0.82 A1-1 (38 mol % 75 3.1 0.78 022 ethylene) 309 From EVOH D   25μm 0 0.1 0.03 EP- (29 mol % 75 1.41 0.35 A1-1 ethylene) 75 022 309 FromBlend:   25 μm 0 0.61 0.15 EP- EVOH D 75 6.79 1.70 A1-1 70% 75 5.6 1.4022 ethylene- 309 acrylate 20% Reaction product of ethylene- acrylate-acid terpolymer with polyamide 10%

[0143] It is apparent that the oxygen transmissions of the films fromEVOH and ethylene-vinyl acetate copolymer were near to those of EVOHalone.

[0144] This is particularly surprising in the light of the comparativelypoor barrier properties of ethylene-vinyl acetate copolymers alone.

[0145] Compared with the film described in EP-A1-1 022 309 andcomprising EVOH with a ethylene-methyl acrylate copolymer and with areaction product made from a terpolymer of ethylene, methyl acrylate andpolyamide, the values obtained are better. It has to be taken intoaccount here that the EVOH used here had higher ethylene content, and itis to be expected that this will give somewhat poorer values than EVOHwith lower ethylene content.

[0146] The films of the present invention make it markedly simpler toachieve stretchablity than is stated in EP-A1-0 483 695, for example,where use has to be made of multi-ply films comprising EVOH withmodified polyolefins, and of reaction products with polyamide. TABLE 4Examples 14 to 18 (Extrusion) Methods similar to that of Examples 1 to13 Oxygen trans- mission Thick- Relative cm³/ Experiment Material nesshumidity (m²d bar) 14a EVOH 50 μm — — comparison 14b EVOH 20 μm  0% 2-3comparison 100%  70 15 EVOH 85% 20 μm — — Levapren ®700 HV 15% 16a EVOH85% 50 μm  0% 0.8-1.5 Levapren ®800 HV 100%  35 15% 16b EVOH 85% 20 μm —— Levapren ®800 HV 15% 17a EVOH 85% about 50 — — EVM 95 15%   μmRoll-milled blend 17b EVOH 85% 20 μm — — EVM 95 15% Roll-milled blend18a EVOH 85% 50 μm — — L 800HV 15% Mixture extruded twice 18b EVOH 85%20 μm — — L 800 HV 15% Mixture extruded twice

[0147] Example 16 repeats Example 3 and confirms the oxygentransmissions found. TABLE 5 Extrusion Examples 14-18: Mechanical valuesfor films of thickness 20 μm Tensile Tensile stress strain Tensile atbreak at Example Material Thickness strength MPa break % 14b EVOH 20 μm55 — 25 comparison 15 EVOH 85% 20 μm 44 48 190 Levapren ®700 HV 15% 16bEVOH 85% 20 μm 55 47 168 Levapren ®800 HV 15% 17b EVOH 85% 20 μm 77 79231 EVM 95 15% Roll-milled blend 18b EVOH 85% 20 μm 102 102 277Levapren ®800 HV 15% Mixture extruded twice

[0148] The results are shown in FIG. 1, which gives the mechanicalvalues from the films of 20 μm thickness from Examples 14-18:

[0149] 14: EVOH alone

[0150] 15: 75% Levapren®700 HV

[0151] 16: 15% Levapren®800 HV

[0152] 17: EVM 95 alone

[0153] 18: 15% Levapren®800 HV, extruded twice

[0154] Alongside the good oxygen barrier properties reported for thefilms of the invention made from EVOH and ethylene-vinyl acetatecopolymers, the tensile strain tests on these films in turn showedmarkedly improved stretchability without any substantial loss ofstrength. This, too, is surprising, since the ethylene-vinyl acetatecopolymers used as blend partner can hardly be regarded as elastomers ofthe type given in the literature (EP-A1-0 722 850, EP-A1-0 761 477),where the classes of elastomer given, e.g. butyl rubber, SEBS and EPDM,have low polarity and glass transition temperatures well below 30° C.

[0155] The EVMs to be used in the films of the invention can certainlyhave glass transition temperatures around room temperature and higherwithout loss of the flexibility and improved stretchability of thefilms.

[0156] The EVOH/EVM films used here were studied by DSC. TABLE 6 MeltingExample Material Tg Tmelt endotherm 1 31 μm 49° C. 165° C. 76 J/gcomparison EVOH 3 Blend 39° C. 161° C. 51 J/g 85% EVOH 15% Levapren ®800 HV 12 Levapren ®400 −31° C.         13° C. and 44° C. 30 J/g 6 Blend44° C. 162° C. 62 J/g 85% EVOH 15% Levapren ®400 4 Blend 44° C. 162° C.56 J/g 70% EVOH 30% Levapren ®800 HV 10 Levapren ®800 0.7° C.  — — HV 9EVM 95 34° C. — — 11 Levapren ®700 −16° C.   — — HV

[0157] Some of the films comprising EVOH showed a weak endotherm at 100°C., attributable to the liberation of bound water.

[0158] It was apparent that when crystalline EVM was used as filmcomponent with EVOH the result was EVA melting endotherm of only veryweak character. Similarly, the glass transition points for the EVM blendpartners were hardly discernible.

[0159] This indicates some degree of compatibility, but without thepresence of miscibility. It appears that the ethylene-vinyl acetatecopolymers of the invention become finely distributed in the EVOH, whileno substantial clouding is observed.

[0160] Furthermore, the melting endotherm of the EVOH is hardly affectedby the addition of EVM. It is clearly advantageous that the EVM of theinvention increases the flexibility to the desired degree, but at thesame time does not reduce the crystallinity of the EVOH, the resultbeing that high permeation barriers are retained.

[0161] Experimental Examples of Production of Multilayer Films:

[0162] Materials used for the experiments

[0163] Eval® L101B: Ethylene-vinyl alcohol copolymer with ethylenecontent of 27 mol % and MFI of 3.9 to ASTM 1238 (210° C., 2 160 g)(available from Kuraray).

[0164] Eva® F101B: Ethylene-vinyl alcohol copolymer with ethylenecontent of 32 mol % and MFI of 3.8 to ASTM 1238 (210° C., 2 160 g)(available from Kuraray).

[0165] Eval® G 156B: Ethylene-vinyl alcohol copolymer with ethylenecontent of 47 mol % and MFI of 14.7 to ASTM 1238 (210° C., 2 160 g)(available from Kuraray).

[0166] Soarnol® DT2903: Ethylene-vinyl alcohol copolymer with ethylenecontent of 29 mol % and MFI of 3.2 to ASTM 1238 (at 210° C.) (availablefrom Nippon Gohsei)

[0167] Soarnol® AT4403: Ethylene-vinyl alcohol copolymer from thecompany Nippon Gohsei with ethylene content of 44 mol %. and MFI of 3 toASTM 1238 (at 210° C.).

[0168] Soarnol® H4815: Ethylene-vinyl alcohol copolymer with ethylenecontent of 48 mol %. and MFI of 16 to ASTM 1238 (at 210° C.) (availablefrom Nippon Gohsei)

[0169] EVOH-30: Ethylene-vinyl alcohol copolymer with ethylene contentof 30 mol %. and MFI of 10 to ASTM 1238 (at 210° C.)

[0170] Levamelt® 800: Ethylene-vinyl acetate copolymer with vinylacetate content of 80% by weight and MFI of 4-5 to ASTM 1238(availablefrom Bayer AG).

[0171] Vestamelt® 722: Polyamide copolymer with MFI of 300 to ASTM 1238(160° C., 2.16 kg) and melting point of 107° C. (available from Degussa)

[0172] Vestamelt® 471: Polyamide copolymer with MFI of 20 to ASTM 1238(160° C., 2.16 kg) and melting point of 119° C. (available from Degussa)

[0173] Durethan® C131 F: Polyamide copolymer with melting point of187-191° C. (available from Bayer AG)

[0174] Durethan® B38FKA:Polyamide with melting point of 222° C.(available from Bayer AG)

[0175] Experimental Series A:

[0176] Preparation of blends for barrier layer

[0177] Experimental apparatus: Twin-screw kneader (TSK), model ZSK 53Rotation rate 165 rpm; melt temperature is set by means of thetemperatures in the extrusion zones (200-215° C.)

[0178] Strand extrusion, 2 mm diameter, cooling in water bath at roomtemperature, knife-pelletized.

[0179] In Table 7, C2 is ethylene. TABLE 7 Blends using ZSK machine,throughput 50 kg/h, residence time about 35 s, die temperature 200° C.,14 bar Melt temperature 215° C. for F and G grades, 240° C. for L grade,data in part by weight Blend No. EVOH Proport. EVOH EVM Proport. EVMCompat Proport. Compat. Pellets 1 G156B 85 L800 15 — — Hard 47 mol % C22 F101B 85 L800 15 — — Hard 32 mol % C2 4 L101B 85 L800 15 — — Hard 27mol % C2 5/1 DT2903 80 L800 15 V471 5 Hard 29 mol % C2 5/2 DT2903 80L800 15 V722 5 Hard 29 mol % C2 5/3 DT2903 80 L800 15 CI31F 5 Hard 29mol % C2 6 L101B 70 L800 30 — — Somewhat 27 mol % soft C2 7 L101B- 60L800 40 — — Soft 27 mol % C2 8 L101B 40 L800 60 — — Cold 27 mol % flow,C2 tacky 12 AT4403 85 L450 15 — — Hard 44 mol % C2 13 EVOH- 85 L800 15 —— Hard 30 30 mol % C2

[0180] The pellets obtained were slightly opaque to white.

[0181] In the case of blends 5/1 to 5/3 in Table 7, copolyamides wereadded in order to test whether these can act as compatibilizers. Theblend materials were extruded without difficulty to give strands, andcould be chopped to give pellets after passage through a water bath.Blend 8 in Table 7 had surface tack when its temperature was raised, andexhibited cold flow on storage. Blends with a predominant proportion ofethylene-vinyl acetate copolymer were cooled for further processing,i.e. pellet-feed, or else on-line feed took place into appropriate filmextruders.

[0182] Experimental Series B: Production of Three-Ply Films byCoextrusion

[0183] Three-ply films with layer sequence polyamide/layer B/polyamidewere extruded, layer B being the barrier layer. For layer B use was madeof commercially available EVOH products (comparative examples), or elsethe blends of the invention from experimental series A. The polyamide(PA) is Durethan® B38FKA, a nylon-6 film material from Bayer AG.

[0184] In each case, films of nominal thickness 135 μm were produced forsubsequent biaxial stretching, and films of thickness 48 μm wereproduced for the thermoforming process.

[0185] Data relating to Construction of Experiment:

[0186] 4 extruders, leading to a 3-layer feed block,

[0187] feed block 270° C., die 280° C. at 3 different measurementpoints.

[0188] The layer thicknesses were determined by on-line radiometricthickness measurement, calibration being by means of an off-linemeasurement (micrometer). The thicknesses were primarily varied via theextruder rotation rates and the draw-off rate. The thickness of eachlayer was influenced via controlled switching off and on of therespective layer. The thickness of this layer was determined via thedifference between the thickness prior to and the thickness after theswitching-off or -on of the layer.

[0189] The on-line thickness measurement also served for monitoring theuniformity of the layer thicknesses. The slot die was initially set tomaximum uniformity. TABLE 8 PA EVOH mol % PA layer Ethylene layer madeEVM made from VA % by wt. from B38FK Layer Parts by wt. B38FK A B EVOH:EVM A Film Thick- Materi Thick Thick- Extrusion No. ness al ness nessperformance Use 1 20 μm L101B EVOH 27 8 μm 20 μm Distribution Thermo-Comp mol % not uniform forming No EVM 100:0 2 45 μm L101B EVOH 27 45 μm 45 μm Non-uniform BOPA Comp mol % distribution No EVM 100:0 3 20 μmH4815 EVOH 48 8 μm 20 μm Distribution Thermo- Comp mol % not uniformforming No EVM 100:0 4 45 μm H4815 EVOH 48 45 μm  45 μm Very non- BOPAComp mol % uniform NoEVM distribution 100:0 5 20 μm Blend EVOH 27 8 μm20 μm Uniform Thermo- 4 mol % distribution forming EVM 80% by along thedie weight 85:15 6 45 μm Blend EVOH 27 45 μm  45 μm BOPA 4 mol % EVM 80%by wt. 85:15 7 20 μm Blend EVOH 27 8 μm 20 μm Thermo- 6 mol % formingEVM 80% by wt. 70:30 8 45 μm Blend EVOH 27 45 μm  45 μm BOPA 6 mol % EVM80% by wt. 70:30 9 20 μm Blend EVOH 27 8 μm 20 μm Thermo- 7 mol %forming EVM 80% by wt. 60:40 10 45 μm Blend EVOH 27 45 μm  45 μm BOPA 7mol % EVM 80% by wt. 60:40 11 20 μm Blend EVOH 27 8 μm 20 μm Non-uniformThermo- 8 mol % distribution forming EVM 80% by through non- wt. regularfeed, 40:60 bridging in extruder for B 12 45 μm Blend EVOH 29 45 μm  45μm Fisheyes in BOPA 5/3 mol % edge region, EVM 80% by disappear wt. oncecopolyamide temperature 80:15:5 raised, some holes on chill roll due tomoisture 13 20 μm Blend EVOH 29 8 μm 20 μm Thermo- 5/3 mol % forming EVM80% by wt. copolyamide 80:15:5 14 45 μm Blend EVOH 44 45 μm  45 μmFisheyes in BOPA 12 mol % edge region EVM 45% by wt. 85:15 14b 20 μmBlend EVOH 44 8 μm 20 μm Thermo- 12 mol % forming EVM 45% by wt. 85:15

[0190] The films were produced with a casting roll temperature of from80 to 100° C., passed through on-line thickness measurement and wound-upafter edge-trim.

[0191] Viscosities of EVOHs Used and of Blends From Experimental SeriesA:

[0192] The shear rate during extrusion processes for films or thinmoldings through dies is in the range from 1 bis 100 s⁻l. For goodextrusion, materials with low viscosities are preferred. The viscositiesof blends with various EVM contents are therefore measured with optimumextrusion shear rates, as shown in Table 9.

[0193] As Table 9 shows, the higher the percentage content of EVM in theblend, the lower the viscosity compared with EVOH alone. TABLE 9: Blend% proportion of Levamelt ® Viscosity η* at No. 800 in blend with L101B300 s⁻¹ in Pa.s — 0 800 4 15 620 6 30 420 7 40 400 8 60 290 — 100 150

[0194] Viscosity η* in Pa.s is measured as a function of shear rate(given as angular velocity omega in 1/s).

[0195] The specimens were first dried for more than 16 hours at 80° C.in a vacuum cabinet and then pressed to give test specimens, using thelaboratory press at 200° C. The measurements were carried out in theARES oscillation rheometer from the company Rheometric, usingplate-plate geometry PP25 in the frequency range from 10 to 0.1 Hz andat temperatures of from 180° C. to 260° C.

[0196] Experimental Series C:

[0197] Stretching experiments for the manufacture of biaxially orientedpolyamide (BOPA) multilayer films.

[0198] Simultaneous bi-axial stretching. TABLE 10: Experimental filmRoll No. 2 6-I 6-II 6-III 6-IV 6-V 6-VI 6-VII 6-VIII 8-I 8-II Framewidth Longitudinal (mm) 750 750 500 500 375 375 375 500 500 500 625Transverse (mm) 625 625 500 500 375 375 375 500 500 500 625 Specimensize Longitudinal (mm) 250 250 250 250 250 250 250 250 250 250 250Transverse (mm) 250 250 250 250 250 250 250 250 250 250 250 Stretchingconditions Stretching 230 240 250 240 240 240 230 230 230 230 230temperature (° C.) Preheat time (s) 90 120 150 120 120 180 120 120 150180 180 Control square on stretched film Longitudinal (mm) 3 3 2 2 1.51.5 1.5 2 2 2 2.5 Transverse (mm) 2.5 2.5 2 2 1.5 1.5 1.5 2 2 2 2.5Experimental film Roll No. 8-ILa 8-III 8-IV 8-V 2-Ib 2-IIb 4-I 4-II 14-I14-I 14-III Frame width Longitudinal (mm) 625 625 500 500 500 500 500500 500 500 500 Transverse (mm) 625 625 500 500 500 500 500 500 500 500500 Specimen size Longitudinal (mm) 250 250 250 250 250 250 250 250 250250 250 Transverse (mm) 250 250 250 250 250 250 250 250 250 250 250Stretching conditions Stretching 230 235 235 230 230 225 225 225 225 230230 temperature (° C.) Preheat time (s) 180 180 180 180 180 180 180 210180 180 120 Control square on stretched film Longitudinal (mm) 2.5 2.5 22 2 2 2 2 2 2 2 Transverse (mm) 2.5 2.5 2 2 2 2 2 2 2 2 2

[0199] TABLE 11: Barrier layer EVOH mol % Optical ethene proper- EVM %by wt. Prior ties VA optical after BOPA Parts by wt. proper- stretch-No. EVOH: EVM ties ing Remark 2 EVOH 27 mol % transp. Film tore usingthe No EVM initial conditions, Comparison no stretching achieved.Temperature increased to 240° C., heating time lengthened to 120 s 6-IEVOH 48 mol % opaque transp. Film tore, No EVM temperature increasedComparison to 250° C. and heating time lengthened to 150 s 6-II As for6-I opaque transp. Yellowing of film 6-III As for 6-I opaque transp.Film break-off 6-IV As for 6-I opaque transp. Film stretchable withouttearing but some cloudiness, appearance somewhat inhomogeneous 6-V Asfor 6-I opaque transp. Film stretchable without tearing, some holesfound, some cloudiness, appearance somewhat inhomogeneous, film hastraces of imprints, therefore subsequent films cleaned with acetone 6-VIAs for 6-1 opaque transp. Film stretchable without tearing. Unstretchedareas are detectable, and the stretching ratio can therefore be furtherincreased 6-VII As for 4 opaque transp. Repeat, further stretchingpossible 6-VIII As for 4 opaque transp. Further stretched, but still notstretched to maximum 8-I EVOH 27 mol % opaque transp. Not yet stretchedto EVM 80% by wt. maximum 85:15 8-II As for 8-I opaque transp. Break-off8-IIa As for 8-I opaque transp. Break-off, temperature not high enough8-III As for 8-I opaque transp. Film break-off, stretching ratio has tobe lowered somewhat 8-IV As for 8-I opaque transp. Film break-off,temperature may be too high 8-V As for 8-I opaque transp. Incipienttearing of film 2-Ib EVOH 27 mol % transp. cloudy, Incipient tearing ofNo EVM film, phase Comparison separation 2-IIb EVOH 27 mol % transp.cloudy Film does not tear, No EVM layer structures, Comparison‘scimitar’ 4-II EVOH 48 mol % transp. cloudy No incipient tearing, NoEVM but phase separation Comparison 4-II EVOH 48 mol % transp. cloudy Noincipient tearing, No EVM film becomes cloudy, Comparison very streaky,phase separation 14-I EVOH 44 mol % opaque No incipient tearing, EVM 45%by wt. film somewhat streaky 85:15 14-II EVOH 44 mol % opaque Someincipient EVM 45% by wt. tearing, some flow 85:15 structures 14-III Asfor 14-III opaque Some incipient tearing, some flow structures

[0200] Oxygen Transmission Values:

[0201] These oxygen transmission values were determined by means of anOX-TRAN device from the company Mocon, with electrochemical O₂ detector.Test parameters: Pressure: 1000 mbar 0₂ Gas moisture: dry Temperature:23 degrees Celsius

[0202] TABLE 12: Barrier layer EVOH mol % ethene Gas EVM % by wt. Totaltrans- VA film mission Film Layer Parts by wt. thick- cm³/m² No. BEVOH:EVM ness 24 h bar 1 L101B EVOH 27 mol % 44.7 about 1 — Comp ethene44.6 about 1 No EVM 100:0 2 L101B EVOH 27 mol % 36 about 1 BOPA afterComp ethene 23 about 1 stretching No EVM BOPA No. 2 100:0 3 H4815 EVOH48 mol % 45.2 8.5 — Comp ethene 46.6 8.6 No EVM 100:0 4 H4815 EVOH 48mol % 28 17 BOPA after Comp ethene 25 16 stretching No EVM BOPA No. 4100:0 5 Blend EVOH 27 mol % 46.2 about 1 — 4 ethene 42.7 about 1 EVM 80%by wt. VA 85:15 6 Blend EVOH 27 mol % 22 about 1 BOPA after 4 ethenestretching EVM 80% by wt. BOPA No. 6 VA 85:15 7 Blend EVOH 27 mol % 43.4about 1 — 6 ethene 44.4 about 1 EVM 80% by wt. VA 70:30 8 Blend EVOH 27mol % 18 23 BOPA after 6 ethene stretching EVM 80% by wt. BOPA No. 8 VASpecimen non- 70:30 regular in nature 9 Blend EVOH 27 mol % 47.5 about 1Thermo- 7 ethene 42.4 about 1 forming EVM 80% by wt. VA 60:40 11 BlendEVOH 27 mol % 39.7 30 — 8 ethene 39.5 30 EVM 80% by wt. VA 40:60 13Blend EVOH 29 mol % 46.7 about 1 BOPA 5/3 ethene 43.5 about 1 EVM 80% bywt. VA Copolyamide 80:15:5 14 Blend EVOH 44 mol % 29 11 BOPA after 12ethene 32 11 stretching EVM 45% by wt. BOPA No. 14 VA 85:15 14b BlendEVOH 44 mol % 47.0 6.6 — 12 ethene 43.5 6.1 EVM 45% by wt. VA 85: 15

[0203] For certain specimens the entry “about 1” is given because thehigh oxygen barrier meant that it was impossible to determine oxygentransmission precisely and unambiguously during the test time. However,the actual values are below this value.

[0204] Thermoformability:

[0205] The thermoformability of the films was determined qualitativelyby way of an apparatus in which a piece of film of about 10×10 cm wasclamped into a frame, heated by means of an IR lamp, and then drawn byvacuum into a mould composed of a rounded stepped pyramid (4 steps of1.5 cm height). This gave a variety of strain levels.

[0206] It was found that the films of the present invention could bethermoformed to give transparent, thin layers, whereas the comparativefilms tended to become optically inhomogeneous (phase separation) athigh strain levels.

[0207] Film 4: White streaks formed, cloudy areas in the direction ofstrain

[0208] Film 6: Initially cloudy film becomes transparent in thethermoformed regions

[0209] Behavior of films 6, 8 and 14 similar to that of film 6

[0210] Morphology of Resultant Films:

[0211] Studies by TEM (transmission electron microscopy) after RuO₄contrasting.

[0212] The following films were used here and in each case themorphology of the inner barrier layer was studied, using magnificationsof 3 500 and 10 000.

[0213] Film 4 (comparison): No structuring detectable

[0214] Barrier Layers with EVOH and EVM (80% by Weight of Vinyl Acetate)

[0215] Film 5: elongate particles (EVM, proportion 15% by weight) ofabout 0.5×5 μm and smaller

[0216] Film 7: elongate particles or elongate lamellae of about 1 μm(EVM proportion 30% by weight)

[0217] Film 8 after stretching: oval particles to some extent withinclusions of EVOH up to about 2 μm (EVM proportion 30% by weight)

[0218] Film 9: elongate lamellae up to 2 μm thickness and smallparticles with diameter of from 0.4 to 1 μm (EVM proportion 40% byweight)

[0219] Film 11: EVM forms the continuous phase with EVOH particles ofsize 2 μm (EVM proportion 60% by weight)

[0220] Barrier Layers with EVOH and EVM (80% by Weight of Vinyl Acetate)and Copolyamide (Copa)

[0221] Film 13: spherical particles of size from 0.4 to 1 μm (EVMproportion 15% by weight, 5% by weight of Copa)

[0222] Barrier Layers with EVOH and EVM (45% by Weight of Vinyl Acetate)

[0223] Film 14: spherical particles of size from 0.2 to 0.8 μm, withrelatively narrow distribution

[0224] Assessment of Films From Experimental Series B

[0225] Films 1 to 4 (comparison) were transparent and their visualassessment was comparable with that of films of similar thickness madefrom polyamide alone.

[0226] Films 5 to 14b are opaque to slightly cloudy, the thick films(intended for stretching) being markedly less transparent than thethinner variants.

[0227] Greater proportions of blend partner in the barrier layer led tomore marked cloudiness.

[0228] All of the films were macroscopically homogeneous. Due toirregularities in pellet feed (tackiness of pellets), film 8 was alwaysobtained with non-regular barrier layer thickness.

[0229] Film 12 had holes, and these could be attributed to moisture inthe blend material.

[0230] Film 14 had fisheyes in the edge region. These could beeliminated by varying the temperature.

[0231] When comparison is made with the comparative films, markedlybetter extrusion is observed using the blends of the present invention.The addition of ethylene-vinyl acetate copolymer has a favorable effecton viscosity behavior during cast film production.

[0232] Assessment of Viscosity of EVOH's used and of the Blends of theInvention:

[0233] When comparison is made with EVOH alone, the ethylene-vinylacetate copolymer Levamelt® 800 exhibited much more marked viscositylowering through shear (shear thinning). The admixture of Levamelt intothe EVOH (blends 3, 6, 7 and 8) led to marked shear thinning in themixture, although the Levamelt was merely present as a separate phasedispersed in the EVOH matrix. The result of this was easier extrusion ofthe blends of the invention when comparison is made with EVOH alone,particularly under the conditions of film extrusion, where the materialhas to pass uniformly through very narrow gaps.

[0234] Assessment of Stretching in Experimental Series C:

[0235] Closer inspection of the films showed that all of the comparativefilms were transparent prior to stretching, but after stretchingappeared non-regular in structure. The stretched areas of thesecomparative films were either cloudy or had tears due to separation ofthe plies.

[0236] The films with the barrier layer of the invention becametransparent as a result of stretching. In all of the stretchingexperiments, the setting of the ideal stretching conditions requiredprolonged trials and was markedly dependent on temperature. No variationin the stretching rate was made at this stage. There remains apossibility of further optimization to give greater stretching ratios,since there is some indication that the films of the invention with thebarrier blends had not been stretched to the maximum.

[0237] The optical properties of the comparative films became poorerafter stretching, and this could be attributed to phase separation,which is not observed with the films of the invention. The criterion ofcontact transparency was always complied with.

[0238] Assessment of Oxygen Transmission:

[0239] It was found that when the stretched films were compared with thefilms of the same composition, their oxygen transmission could becalculated from the thickness.

[0240] Compared with the films with the barrier layers of EVOH alone,the films of the invention have unchanged, excellent barrier values. Theoxygen transmissions begin to rise only when the admixture ofethylene-vinyl acetate copolymer reaches 60% by weight. The proportionof ethylene-vinyl acetate copolymer in the barrier layer shouldtherefore not substantially exceed 50% by weight.

[0241] A conclusion which may be drawn is that in the blends made fromEVOH and EVM with proportions of up to at least 40% by weight of EVMthis was present in the form of a discontinuous phase. In a matrix madefrom EVOH, the EVM formed particles of elongate shape. Increasing theproportion of EVM led to structures, which were to some extent lamellar,and this is advantageous for retention of barrier properties. Afterstretching, involving a heat-conditioning step, the shape of the EVMparticles changed in that the lamellar particles become particles whoseshape is rather spherical. The formation of the discrete EVM phasewithin the EVOH phase in the multilayer product of the inventionprovides a good basis for the stretching/thermoforming of the barrierlayer. The matrix made from EVOH determines the barrier properties here.

[0242] If, as in film 11, the proportion of EVM markedly exceeds that ofEVOH, phase inversion occurs. It could be assumed that layers of thistype have lost the barrier properties typical of EVOH.

[0243] In film 13 the effect of adding a copolyamide as compatibilizercould be observed. Spherical particles were obtained. It may be assumedthat this phase morphology remains stable even through stretching andheat-conditioning processes.

[0244] Finally, in film 14 the effect of using a less polar EVM wasobserved. Here, the EVM has particularly fine distribution.

[0245] Particular stabilization of the distribution of the EVM could beachieved by adding copolyamides as third component in the barrier layer.The stability of the morphology could be secured by this method duringmultiple processing (use of recycled material) and duringheat-conditioning. The result was retention of fine-particle dispersionof the EVM in the EVOH matrix, and thus transparency was ensured.

[0246] The better stretchability of the films with the barrier layers ofthe invention is particularly noticeable when using the EVM grade with80% by weight of vinyl acetate, and less noticeable when using the EVMgrade with 45% by weight of vinyl acetate. This may be connected to thehighly extended structure of the EVM phase, which has a particularlynoticeable flexibilizing effect.

[0247] The result for the person skilled in the art was therefore theability to optimize flexibility properties, and in particularstretchability in the composite with PA and secondly the establishmentof smaller particle sizes for the EVM phase. This permitted control oftransparency and of morphological stability. Factors, which should beregarded as significant here, are the selection of the EVM and theaddition of copolyamides.

[0248] Although the invention has been described in detail in theforegoing for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be limited by the claims.

What is claimed is:
 1. A single- or multilayer film comprising α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the α-olefin vinyl acetate copolymer has vinyl acetate repeat units present in the range from 35 to 99.99% by weight.
 2. The film according to claim 1, wherein the α-olefin is selected from ethylene, propene, n-butene, i-butene, pentene, hexene, 1-hexene, heptene, octene, 1-octene and mixtures of these.
 3. The film according to claim 1, wherein the α-olefin-vinyl acetate copolymer contains at least 45% by weight of vinyl acetate repeat units.
 4. The film according to claim 3, wherein the α-olefin-vinyl acetate copolymer contains at least 65% by weight of vinyl acetate repeat units.
 5. A process for producing a single film having α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the α-olefin vinyl acetate copolymer has vinyl acetate repeat units present in the range from 35 to 99.99% by weight comprising the step of mixing the copolymer in a mixer with additional constituents.
 6. Multilayer film having α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the α-olefin vinyl acetate copolymer has vinyl acetate repeat units present in the range from 35 to 99.99% by weight, wherein the multilayer film comprises at least one layer A and at least one layer B, wherein, A comprises a thermoplastic polymer and B comprises an α-olefin-vinyl alcohol copolymer and an α-olefin-vinyl acetate copolymer whose vinyl acetate content is in the range from 35 to 95% by weight.
 7. Multilayer film according to claim 6, wherein the thermoplastic polymer is polyamide or polypropylene.
 8. Multilayer film according claim 6, wherein the α-olefin-vinyl alcohol copolymer is ethylene-vinyl alcohol copolymer having an ethylene content in the range from 20 to 75 mol %.
 9. Multilayer film according to claim 6, wherein the α-olefin-vinyl acetate copolymer is ethylene-vinyl acetate copolymer.
 10. Multilayer film according to claim 6 having a layer sequence of A,B,A.
 11. Multilayer film according to claim 10, wherein the layer sequences is polyamide, layer B, polyamide.
 12. Multilayer film according to claim 10, wherein the layer sequence is polypropylene, layer B, polypropylene.
 13. Multilayer film according to claim 6, wherein layer B comprises additionally up to 25% by weight of a copolyamide with a melting point in the range from 70° to 200° C.
 14. Multilayer product according to claim 12, wherein the layer sequence is polypropylene, layer B, polypropylene and wherein a polymer suitable to improve the cohesion is between each pair of layers.
 15. Process for producing the multilayer film having α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the α-olefin vinyl acetate copolymer has vinyl acetate repeat units present in the range from 35 to 99.99% by weight comprising the step of coextruding the film of the α-olefin-vinyl acetate copolymer/α-olefin-vinyl alcohol copolymer.
 16. Process for producing the multilayer film having α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the α-olefin vinyl acetate copolymer has vinyl acetate repeat units present in the range from 35 to 99.99% by weight comprising the step of laminating the film of the α-olefin-vinyl acetate copolymer/α-olefin-vinyl alcohol copolymer.
 17. Packaging material comprising the single- or multilayer film having α-olefin-vinyl alcohol copolymers and at least one α-olefin-vinyl acetate copolymer, wherein the α-olefin vinyl acetate copolymer has vinyl acetate repeat units present in the range from 35 to 99.99% by weight. 